The proposed experiments are designed to study the action of thyrotropin releasing hormone on electrically induced seizures and long-term potentiation. Electrical stimulation of the afferent pathways to the CA1, CA3, and dentate granule cells will occur in the presence and absence of TRH. Detailed dose-response curves will be established in an attempt to determine if TRH alters either LTP or seizure induction. Additionally, the action of TRH on the ventral vs. the dorsal hippocampus will be contrasted. TRH receptors exist in a high concentration in the ventral hippocampus (CA3) and ventral dentate gyrus. The long-term objectives of this project are related to the possible actions of TRH in maintenance of overall excitability of the nervous system, in the control of seizure activity, and influence on memory formation. TRH is well known to control human behavior indirectly through its action on the pituitary and thyroid gland. The question of whether or not TRH directly controls the excitability of the brain remains to be determined. These studies will eventually need to include young, middle-aged and old rats of both sexes.